Conventional cathode ray tube (CRT) displays rely on an electron beam that sweeps over a phosphor-coated display surface on the inside of the tube to form an image. Different phosphors are stimulated by the high-energy electrons to emit different colors of light, for example red, green, and blue corresponding to pixels in the displayed image. Phosphors are also commonly used with solid-state light-emitting diodes to emit white light. For example, a blue-light emitting diode (LED) coated with phosphors that absorb a portion of the emitted blue light and emitted yellow light appears white to the human visual system. Similarly, organic light-emitting diode (OLED) illumination devices using phosphors are described in WO 2010032603.
Flat-panel light-emitting diode (LED) displays that incorporate luminescence-converting elements (such as phosphors) are described in U.S. Pat. No. 5,994,722. Alternatively, OLED displays can employ a single high-frequency light emitter together with color-conversion materials (also known as color-change materials) to provide a variety of color light output. The color-conversion materials absorb the high-frequency light and re-emit light at lower frequencies. For example, an LED or OLED device can emit blue light suitable for a blue sub-pixel and employ a green color-conversion material layer to absorb the blue light to emit green light and employ a red color-conversion material layer to absorb the blue light to emit red light. The color-conversion materials can be combined with color filters to further improve the color of the emitted light and to absorb incident light and avoid exciting the color-conversion materials with ambient light, thereby improving device contrast. Light-scattering phosphorescent or fluorescent particles excited by organic light-emitting diodes (OLEDs) are described in U.S. Pat. No. 7,834,541. U.S. Patent Pub. No. 20050116621 A1 entitled Electroluminescent devices and methods of making electroluminescent devices including a color conversion element also describes the use of color-conversion materials.
Layers having color-conversion materials can be combined with scattering particles to enhance the performance of the color-conversion materials by increasing the likelihood that incident light will interact with the color-conversion materials, thereby reducing the concentration or thickness of the layer. Such a combination may also prevent light emitted by the color-conversion material from being trapped in the color-conversion material layer. U.S. Pat. No. 7,791,271 describes a top-emitting OLED with color conversion materials and U.S. Pat. No. 7,969,085 discloses a color change material layer. U.S. Patent Pub. No. 20050275615 A1 entitled Display device using vertical cavity laser arrays describes such a layer as does U.S. Patent Pub. No. 20040252933 entitled Light Distribution Apparatus. U.S. Patent Pub. No. 20050012076 entitled Fluorescent member, and illumination device and display device including the same teaches the use of color-conversion materials as scattering particles. U.S. Patent Pub. No. 20040212296 teaches the use of scattering particles in a color-conversion material layer to avoid trapping the frequency-converted light. Diffusers are also useful in increasing the viewing angle of display pixels. U.S. patent application Ser. No. 11/361,094, filed Feb. 24, 2006, entitled Light-Scattering Color-Conversion Material Layer describes integral light-scattering color-conversion material layers.
Flat-panel displays typically rely on thin-film semiconductor structures to provide control signals that control the pixels in the flat-panel display. However, such thin-film structures have relatively low performance when compared to crystalline semiconductor structures typically used in integrated circuits. Furthermore, LED emitters, and especially micro-LED emitters have a relatively small light-emitting area and aperture ratio when used in flat-panel displays. Color-conversion layers coated over an entire flat-panel substrate are therefore wasteful since most of the layer is not excited by light-emission from the LEDs. Patterning the substrate at the resolution needed with micro-LEDs is difficult and the use of larger LEDs that are individually coated with color-conversion material limits the resolution of the flat-panel display.
There is a need, therefore, for devices, systems and methods for providing color-conversion structures in combination with micro-LEDs in a flat-panel display that enable high resolution, effective use of color-conversion material, and excellent performance efficiency, viewing angle, and colors.